The present invention relates to a yarn processing system
Yarn processing systems, which the invention refers to, may be not only yarn feeders, but e.g. also accessory devices used for yarn processing that supply textile machines, such as weaving or knitting machines, with yarn and comprise at least one electrically driven component and a control circuit assigned thereto. Apart from yarn feeders, such devices may be yarn impregnating means or yarn lubricators, controlled yarn brakes and yarn tensioners, slip-type conveyors for yarn, rotary drives for yarn supply coils, or the like. The control circuit may be positioned in the housing of the yarn feeder or the accessory device, or in a separate housing of the yarn feeder or the accessory device, or in a separate housing which, nevertheless, has to be regarded as part of the yarn processing system.
In a yarn feeder known from DE-C-265 18 57, the control circuit of the drive motor comprises effect transistors as semiconductor components. The control circuit is normally arranged in the housing, with the effect transistors being positioned on the printed circuit board. During operation the semiconductor components generate heat which during prolonged operation leads to a relatively high heat level that impairs the service life of the control circuit, in particular of the semiconductor components.
In yarn feeders it is known from prior use in practice (FIG. 1) that heat-generating semiconductor components, such as effect transistors, are positioned on the edge portion of the printed circuit board and that a strip-like heat conducting body is mounted in the housing or on the printed circuit board in the vicinity of the semiconductor components, with portions of the semiconductor components being pressed against said heat conducting body by clamping elements. The heat conducting body, in turn, is mounted in heat transmitting contact with the housing.
This is troublesome from a constructional point of view and, with respect to the equipment of the printed circuit board, requires inexpedient upright positions of the semiconductor components because the latter must project upwards from their bondings with the printed circuit board to contact the heat conducting body. Moreover, contact with the heat conducting body is established some distance away from the hottest portion of the semiconductor component which normally lies near the bondings and thus radiates a lot of heat into the environment, said heat being not absorbed by the heat conducting body. The inexpensive so-called xe2x80x9csurface mountingxe2x80x9d, e.g. by assembling robots, can therefore not be employed for said semiconductor components. In this expedient mounting technique, semiconductor components are secured in a lying position with one of their surfaces to an adhesive surface of the printed circuit board, i.e. either in addition to the bondings or even for creating a bonding or grounding.
It is known from EP-A-0 116 396 that electronic subassemblies which can be stacked one upon the other are each designed such that two rigid plates consisting of heat-conducting metal clamp a printed circuit board with semiconductor components arranged thereon between themselves. The two outer plates are urged together by C-clips provided at the edge side or by clamping screws. At least one plate has provided thereon projections which extend through openings into the printed circuit board from below up to the semiconductor components. Since the plates substantially correspond to the printed circuit board in size, their heat absorbing capacity is limited.
US-5-A-812 375, which is of an older time rank, suggests an electronic subassembly which consists of at least one printed circuit board equipped with semiconductor components and of an encapsulation consisting of two shells, the base of the encapsulation consisting of heat conducting material and comprising at least one projection that projects into an opening of the printed circuit board up to the neighborhood of an insulating layer carrying a semiconductor component to be cooled. Said encapsulated subassembly forms a unit in which the base of the encapsulation has only a limited heat absorbing capacity.
It is the object of the present invention to provide a yarn processing system of the above-mentioned type in which a low temperature level can be obtained in the control circuit in a constructionally simple, inexpensive and space-saving way, optionally even by applying the surface mounting technique for the semiconductor components.
Heat generated by the semiconductor component is dissipated in a highly efficient manner by physical heat transmission through the printed circuit board into the housing or housing part. The projection can easily be shaped during formation of the housing. The semiconductor component is cooled in a particularly expedient manner near the bondings, i.e. near the place of origin of heat, because the prolongation can extend through the printed circuit board to the place of origin. Heat accumulation between the semiconductor component and the printed circuit board is also avoided because a physical heat conducting path is created, extending from the semiconductor component into the housing. The temperature of the semiconductor component and the control circuit can thereby be reduced considerably, which is of benefit to operational safety and to the service life of the control circuit. The housing may be the housing of the yarn feeder or of an accessory device, which as the housing of the yarn processing device has a very high heat absorbing capacity thanks to its size and mass.
The prolongations forming the heat dissipating body are e.g. block- or pin-shaped, which is simple with respect to technical production, and are integral with the housing or housing part. The prolongations can already be realized during formation of the housing or housing part, which will considerably simplify assembly at a later time. The prolongation expediently penetrates through an opening or cutout of the printed circuit board, which has specifically been formed for said purpose, the prolongation engaging into the opening or cutout in a relatively accurately fitting manner or with a play on all sides. In the case of large semiconductor components several prolongations could perform a joint cooling action.
An intermediate material which is inserted between the semiconductor component and the prolongation and which is suitably elastic at least to some extent improves heat dissipation, for it may be difficult to achieve full contact between hard or metallic surfaces. The intermediate material is capable of compensating for wrong positions caused by the production process or thermally between the heat dissipating surfaces.
Suitably, the intermediate layer is an electrically insulating pad (e.g. gap pad) of a highly heat-conducting material, an adhesive or filler coat (e.g. silicone plastics), or a flexible carrier impregnated with an adhesive agent (e.g. a self-adhesive insulating tape.
Thanks to the prolongation which for cooling purposes extends through the printed circuit board to the semiconductor component (with or without intermediate layer), the semiconductor component to be cooled can advantageously be mounted according to the so-called surface mounting technique on the printed circuit board, i.e. in an automatic mounting device and/or with assembly robots.
Advantageously, the semiconductor component is acted upon by an abutment at the side opposite to the prolongation. This is of advantage for various reasons.
The abutment can produce a force equilibrium in a non-positive manner with the prolongation pressing against the semiconductor components, so that the connection portion of the semiconductor component with the printed circuit board or the bondings is not subjected to any undesired loads. Moreover, the contact pressure between prolongation and semiconductor component can be adjusted by means of the abutment. Finally, the printed circuit board can be positioned and secured in its position within the housing or a housing part by means of the abutment at the same time, so that the number of fastening points for the printed circuit board can be reduced and further fastening points are no longer needed. The abutment may be a positive positioning member for the semiconductor component.
When the abutment is also secured to a holding prolongation of the housing, all forces are received by the housing without any undue load on the printed circuit board or the semiconductor component.
The abutment may be a spring element preferably with adjustable contact pressure, to obtain the above-mentioned equilibrium of forces and to secure the printed circuit board in its position. For instance, the spring element is fixed in abutment against its holding block, so that the hold-down force can be predetermined in an accurate way.
It is advantageous with respect to the mounting technique when a joint abutment is assigned to a plurality of semiconductor components.
As stated, the prolongations define a holding device for printed circuit boards together with the abutment so that further fastening points and mounting steps are not required for fixing the printed circuit board as soon as the mounting steps for cooling have been taken.
In a simple production technique the prolongations are e.g. block- or pin-shaped and integral with the housing or housing part. The prolongations can already be realized during shaping of the housing or housing part, which considerably simplifies the later mounting process.
For achieving an efficient heat transfer during heat dissipation the end faces of the prolongations should be machined. Optionally, the end faces are even adapted to the contours of the semiconductor components in the support area.
A plurality of prolongations of the housing, which serve cooling purposes, may be interconnected by connection webs or contained in a joint base to use a mass which is as large as possible for cooling and heat distribution, respectively, over a short distance.
When a support shoulder for the printed circuit board is provided on at least one of the prolongations, it is easy to position the printed circuit board and to secure the same in its position.